Tires are known in which the tread has circumferential and transverse grooves defining a number of blocks, at least some of which have, on the outer surface, a number of sipes substantially crosswise to the motion direction of the tire. The sipes, which divide the relative blocks into respective numbers of relatively flexible elements crosswise to the motion direction of the tire, serve not only to break up the film of water on wet road surfaces, for better tire-ground contact in the rain, but also, and above all, to trap snow, by flexing, between adjacent elements to improve traction, braking, and lateral stability on snow.
While improving grip of the tire on wet road surfaces or snow, siped blocks, on the other hand, obviously have the drawback—given the flexibility of the relative elements, and especially on dry road surfaces—of impairing tire performance in terms of handling capacity, traction, and braking.
To control deformation of the elements with respect to the adjacent elements when subjected to lateral forces, EP-1 073 562 proposes increasing friction between two surfaces of adjacent elements separated by a sipe, by imparting mating three-dimensional shapes to the surfaces. More specifically, projections are formed on each of the two surfaces, and each engage a respective cavity on the other surface.
Such a solution allows control of transverse deformation of the elements, i.e. along the relative sipes, but not of longitudinal deformation of the elements, i.e. crosswise to the relative sipes.